It is often desirable to provide assistance to a person who is attempting to move from a sitting position in a chair to a standing position. Age, infirmity, or various disabilities often render it difficult for persons to rise out of a chair from a sitting to a standing position without assistance.
In moving the occupant of a chair from a sitting to a free standing position, it is critical that both positions provide adequate and comfortable support if the chair is to function efficiently. The chair should be designed to distribute pressure to the back, buttocks and thighs of a user in the standing position. Also, as the chair moves an occupant from a sitting to a standing position, it is often critical that the chair backrest not apply shear stresses to the back of an occupant. It is very important that the upper leg of the occupant be positioned as the chair rises to support the weight of the occupant in the standing position as weight is transferred from the chair to the legs. Once the legs are properly positioned, then it is desirable for the chair to tilt forward to aid in transferring the weight of the occupant to the occupant's legs.
In the past, the design of chairs which have been developed to move occupants upwardly from a sitting position has been directed toward providing the upward movement and has not concentrated on positioning the legs and torso of the occupant and then tilting the chair for transition from the sitting to the standing position. U.S. Pat. No. 4,249,774 to Andreasson discloses a chair of this type which requires an occupant to slide forward over a projecting seat.
A number of wheelchairs have been developed to raise an occupant from a sitting to a standing position and to support the occupant in the standing position, but these chairs are designed for continued occupant support in a standing position and not to facilitate transition from the chair to a free standing, unsupported position. U.S. Pat. Nos. 5,211,414 and 5,401,044 to Galumbeck are illustrative of wheelchairs of this type.